DESCRIPTION: (Adapted from the application) Propagated vasomotor responses have been shown to be important in regulating microvascular blood flow in response to hyperaemia and to be impaired following ischemia. The investigators found that extraluminally applied purines, including adenosine-triphosphate (ATP), caused a vasoconstriction in cerebral arterioles which surprisingly was converted to a propagated vasodilation. Inhibition of the endothelial nitric oxide (NO) greatly attenuated ATP-induced propagation in these vessels. It is unknown if and how endothelial (EC) and smooth muscle cells (SMC) interact to locally release purines nor is the mechanism of longitudinal communication caused by purines completely understood. The goal of this proposal is to elucidate the mechanism and interdependence of radial (locally between EC and SMC) and longitudinal (along the EC and SMC of a vessel) communication in response to purinergic vasomotor stimulation. The investigator will test three hypotheses: 1) Cellular cross talk between EC and SMC exists in response to purinergic stimulation. Using both isolated arterioles and EC and SMC cultures, the investigator will examine the role of the purinoceptors in the initiation of local responses in both EC and SMC. 2) The endothelium is the medium for propagation in cerebral arterioles. The investigator will investigate whether the endothelium is essential for propagation of vasomotor responses and if this propagation depends on gap junctions to allow for longitudinal cross talk. 3) Nitric oxide availability is necessary for propagation of vasomotor responses. Using cerebral arterioles from normal and endothelial NO synthase deficient (eNOS-) mice, the investigator will examine the importance of NO in the propagation of vasomotor responses. The experiments will be performed in rat isolated cerebral arterioles and eNOS- mouse arterioles in vitro as well as in cultured rat EC and SMC. Local micropressure ejection will be used for stimulation of isolated vessels and cells in culture. Video microscopy will be used for all observations. In blood vessels, the investigator will measure local and propagated diameter and membrane potential responses as well as cellular dye transfer. In cell culture, the investigator will measure local and propagated membrane potential, intracellular calcium activity, and dye transfer. The role of purinoceptors, gap junctions, and EC and SMC in local and propagated response will be revealed with pharmacological intervention as well with endothelial ablation. The significance of NO in the propagation will be demonstrated by supplementing NO in eNOS deficient mouse arterioles.